PORTLAND, Ore. -- A federal judge threw out Oregon's same-sex marriage ban Monday, marking the 13th legal victory for same-sex marriage advocates since the U.S. Supreme Court last year overturned part of a federal ban.

State officials earlier refused to defend Oregon's voter-approved ban in court and said they would be prepared to carry out same-sex marriages almost immediately if the judge struck it down.

McShane joins judges in seven other states who have struck down same-sex marriage bans, though appeals are under way. Lower-court judges have repeatedly cited last year's Supreme Court ruling when striking down bans.

Four gay and lesbian couples brought the Oregon cases, arguing the state's marriage laws unconstitutionally discriminate against them and exclude them from a fundamental right to marriage.

Democratic Attorney General Ellen Rosenblum refused to defend the ban, saying there are no legal arguments that could support it in light of decisions last year by the U.S. Supreme Court. She sided with the couples, asking the judge to overturn the ban, and says she won't appeal.

The judge denied a request by the National Organization for Marriage to defend the law on behalf of its Oregon members. A panel of the U.S. Court of Appeals in San Francisco on Monday refused the group's request for an emergency stay of that decision, allowing same-sex marriages to proceed.

The U.S. Supreme Court last year struck down parts of the 1996 Defense of Marriage Act, which barred the federal government from recognizing same-sex marriage. It determined the law improperly deprived gay couples of due process.